Physics of semiconductor microcavity lasers

The development of the microcavity laser has opened new vistas for exploration in regard to light-matter interaction. Here, we consider several experimental investigations with these smallest of lasers. Injection of an external optical signal into a vertical cavity surface emitting laser (VCSEL) reveals the weak injection regime of frequency locking and the strong injection regime of asymmetric local modification to the semiconductor gain curve. Above laser threshold linewidth measurements allow us to determine the linewidth enhancement factor, in agreement with theory. Below threshold measurements allow us to deduce carrier density and carrier lifetime. The definition of laser threshold in a microcavity laser has recently come under question. Intensity correlation measurements of the light emitted by a VCSEL exhibit a peak at laser threshold. Theoretical calculations confirm the experimental data and further show that this threshold peak remains even as the spontaneous emission rate into nonlasing modes approaches zero.